Document consumer and internal loading flows

docs/internal/overview.md

@@ -87,3 +87,58 @@ operations and CLI ordering. [ADR 0019](../adr/0019-explicit-configuration-disco
 records explicit main-file discovery. The [import internals](imports.md)
 document candidate and namespace identities, discovery and scheduling, and the
 bounded algorithms.
+
+## Implementation flow
+
+The root facade converts caller-owned values into engine-owned requests. The
+ordinary and grouped entry points share a normalized `loadRequest`: see
+[`lifecycle.go`](../../lifecycle.go), [`layered.go`](../../layered.go), and
+[`load_request.go`](../../internal/engine/load_request.go). Load-wide definition,
+version, default-import, and override policy stays distinct from each input's
+source, filesystem, destination, and import settings.
+
+[`acquisition.go`](../../internal/engine/acquisition.go) defines acquisition
+policy and load-wide and per-tier accounting state. Each input is acquired under
+that policy; grouped requests retain acquired underlay scopes until their tier is
+composed in [`load_request.go`](../../internal/engine/load_request.go). Live
+filesystem access handles are confined to acquisition and closed there. Resolved
+filesystem facts used to authorize access are separate from passively retained
+resource contexts: see
+[`filesystem_context.go`](../../internal/engine/filesystem_context.go) and
+[`source_context.go`](../../internal/engine/source_context.go).
+
+Import responsibilities are split across candidate selection and path
+normalization in [`import_selection.go`](../../internal/engine/import_selection.go),
+source reading and traversal admission in
+[`import_acquisition.go`](../../internal/engine/import_acquisition.go),
+directory walking in [`directory_walk.go`](../../internal/engine/directory_walk.go),
+dependency graph scheduling in [`import_graph.go`](../../internal/engine/import_graph.go),
+and projection of acquired evidence into final source coordinates in
+[`import_projection.go`](../../internal/engine/import_projection.go). The
+[import internals](imports.md) page describes the boundaries and identities.
+
+After acquisition handles are closed, grouped composition and inheritance run on
+the retained ordered documents. `inheritance.go` coordinates traversal and
+[`inheritance_schedule.go`](../../internal/engine/inheritance_schedule.go) applies
+dependency-ready templates;
+[`inheritance_prepare.go`](../../internal/engine/inheritance_prepare.go)
+prepares child and parent inputs,
+[`inheritance_combine.go`](../../internal/engine/inheritance_combine.go)
+returns the combined value with its origin, policy, sequence, and diagnostic
+evidence, and [`inheritance_finalize.go`](../../internal/engine/inheritance_finalize.go)
+accounts for and finalizes the result. Projection and schema work have separate
+operation owners: [`value_operation.go`](../../internal/engine/value_operation.go)
+holds per-operation state, [`projection.go`](../../internal/engine/projection.go)
+builds projected values, [`schema.go`](../../internal/engine/schema.go) owns
+descriptor caching and type policy, and
+[`schema_fields.go`](../../internal/engine/schema_fields.go) owns ordinary and
+inline field assembly. [`decode.go`](../../internal/engine/decode.go) consumes
+those descriptors for typed decoding.
+
+Behavioral ownership follows the same handoffs: imports and grouped lifetimes are
+covered by `imports_test.go`, `load_request_test.go`, and focused source,
+discovery, and destination tests; inheritance by the inheritance test files;
+reflection behavior by `schema_test.go`, `projection_test.go`, and
+`decode_test.go`. The [development test map](../development.md#task-to-test-map)
+links focused commands. Typed clone extraction remains deferred in
+[`future.md`](../roadmap/future.md#4-clone-traversal-review).